Dynamic Draft for Fresnel Lenses

ABSTRACT

A lens includes an optically transparent substrate having a first lens surface and a second lens surface opposite to the first lens surface. The first lens surface includes a plurality of Fresnel structures. A respective Fresnel structure of the plurality of Fresnel structures includes a slope facet and a draft facet. The draft facet is characterized by a draft angle. The draft angle of the respective Fresnel structure is based on a distance of the respective Fresnel structure from a center of the lens.

RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No. ______,entitled “Hybrid Fresnel Lens with Reduced Artifacts,” filedconcurrently here with (Attorney Docket Number 010235-01-5085-US) andU.S. patent application Ser. No. ______, entitled “Hybrid Fresnel Lenswith Increased Field of View,” filed concurrently here with (AttorneyDocket Number 010235-01-5086-US), both of which are incorporated byreference herein in their entireties.

TECHNICAL FIELD

This relates generally to optical lenses, and more specifically tooptical lenses used in head-mounted display devices.

BACKGROUND

Head-mounted display devices (also called herein head-mounted displays)are gaining popularity as means for providing visual information touser. However, the size and weight of conventional head-mounted displayshave limited applications of head-mounted displays.

SUMMARY

Accordingly, there is a need for head-mounted displays that are compactand light, thereby enhancing the user's virtual-reality and/or augmentedreality experience.

Fresnel lenses provide apertures and focal lengths comparable toconventional lenses. Because Fresnel lenses are typically thinner andlighter than conventional lenses of similar performance features (e.g.,aperture and/or focal length), replacing conventional lenses inhead-mounted displays with Fresnel lenses can reduce the size and weightof the head-mounted displays. However, Fresnel lenses suffer fromdiffractions and other artifacts associated with Fresnel structures, andthus, their use in imaging applications is limited.

Thus, there is a need for lenses that are compact and light whilereducing optical artifacts associated with such lenses.

The above deficiencies and other problems associated with conventionallenses are reduced or eliminated by the disclosed lens. In someembodiments, the lens is included in a display device. In someembodiments, the device is a head-mounted display device. In someembodiments, the device is portable.

In accordance with some embodiments, a lens includes an opticallytransparent substrate having a first lens surface and a second lenssurface opposite to the first lens surface. The first lens surfaceincludes a plurality of Fresnel structures. A respective Fresnelstructure of the plurality of Fresnel structures includes a slope facetand a draft facet, wherein the draft facet is characterized by a draftangle. The draft angle of the respective Fresnel structure is based on adistance of the respective Fresnel structure from a center of the lens.

In accordance with some embodiments, a display device includes a lensdescribed herein and an array of light emitting devices coupled with thelens for outputting light through the lens.

Thus, the disclosed embodiments provide compact and light weight displaydevices with increased efficiency, effectiveness, and user satisfactionwith such devices.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the various described embodiments,reference should be made to the Description of Embodiments below, inconjunction with the following drawings in which like reference numeralsrefer to corresponding parts throughout the figures.

FIG. 1A is a perspective view of a display device in accordance withsome embodiments.

FIG. 1B is a block diagram of a system including a display device inaccordance with some embodiments.

FIG. 2A illustrates a cross-section of a conventional Fresnel lens.

FIG. 2B illustrates a cross-section of a Fresnel lens with dynamic draftin accordance with some embodiments.

FIG. 2C illustrates surface profiles of a conventional Fresnel lens anda Fresnel lens with dynamic draft in accordance with some embodiments.

FIGS. 2D and 2E illustrate interaction between incoming light and adraft facet in accordance with some embodiments.

FIG. 2F illustrates reduction in interaction between incoming light anda draft facet in accordance with some embodiments.

FIG. 2G shows a cross-sectional view of a Fresnel lens with dynamicdraft in accordance with some embodiments.

FIG. 2H shows optical artifacts caused by a conventional Fresnel lensand a Fresnel lens with dynamic draft in accordance with someembodiments.

FIG. 2I shows optical artifacts caused by a conventional Fresnel lensand a Fresnel lens with dynamic draft in accordance with someembodiments.

FIG. 3A is an isometric view of a display device in accordance with someembodiments.

FIG. 3B is an isometric view of a lens from a first direction inaccordance with some embodiments.

FIG. 3C is an isometric view of the lens shown in FIG. 3B from a seconddirection in accordance with some embodiments.

FIG. 3D shows a plan view and a cross-sectional view of the lens shownin FIG. 3B.

FIG. 3E is a cross-sectional view of a lens in accordance with someembodiments.

FIG. 3F is a cross-sectional view of a lens in accordance with someembodiments.

FIG. 3G shows Fresnel structures of the lens shown in FIG. 3F inaccordance with some embodiments.

FIG. 3H is a cross-sectional view of a lens in accordance with someembodiments.

FIG. 3I is a cross-sectional view of a lens in accordance with someembodiments.

FIG. 3J is a cross-sectional view of a lens in accordance with someembodiments.

FIG. 4A shows an isometric view of a lens in accordance with someembodiments.

FIG. 4B shows a plan view and a cross-sectional view of the lens shownin FIG. 4A.

FIG. 4C shows a cross-sectional view of the lens shown in FIG. 4A.

FIG. 4D shows an isometric view of a cylindrical lens in accordance withsome embodiments.

FIG. 5A illustrates an exemplary surface profile in accordance with someembodiments.

FIG. 5B illustrates an exemplary surface profile in accordance with someembodiments.

FIG. 5C illustrates an exemplary surface profile in accordance with someembodiments.

FIG. 5D illustrates an exemplary surface profile in accordance with someembodiments.

These figures are not drawn to scale unless indicated otherwise.

DETAILED DESCRIPTION

Conventional head-mounted displays are larger and heavier than typicaleyeglasses, because conventional head-mounted displays often include acomplex set of optics that can be bulky and heavy. It is not easy forusers to get used to wearing such large and heavy head-mounted displays.

Fresnel lenses, typically having multiple concentric annular sectionsthat are offset from one another (e.g., for a circular lens), provideapertures and focal lengths comparable to conventional lenses. BecauseFresnel lenses are typically thinner and lighter than conventionallenses of similar performance features (e.g., aperture and/or focallength), replacing conventional lenses in head-mounted displays withFresnel lenses can reduce the size and weight of the head-mounteddisplays. However, Fresnel lenses suffer from diffractions and otherstray light artifacts associated with Fresnel structures, and thus,their use in imaging applications is limited.

The disclosed embodiments provide Fresnel lenses, with dynamic draft,that are compact and light, and reduce optical artifacts.

Reference will now be made to embodiments, examples of which areillustrated in the accompanying drawings. In the following description,numerous specific details are set forth in order to provide anunderstanding of the various described embodiments. However, it will beapparent to one of ordinary skill in the art that the various describedembodiments may be practiced without these specific details. In otherinstances, well-known methods, procedures, components, circuits, andnetworks have not been described in detail so as not to unnecessarilyobscure aspects of the embodiments.

It will also be understood that, although the terms first, second, etc.are, in some instances, used herein to describe various elements, theseelements should not be limited by these terms. These terms are used onlyto distinguish one element from another. For example, a first surfacecould be termed a second surface, and, similarly, a second surface couldbe termed a first surface, without departing from the scope of thevarious described embodiments. The first surface and the second surfaceare both surfaces, but they are not the same surfaces.

The terminology used in the description of the various describedembodiments herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used in thedescription of the various described embodiments and the appendedclaims, the singular forms “a,” “an,” and “the” are intended to includethe plural forms as well, unless the context clearly indicatesotherwise. It will also be understood that the term “and/or” as usedherein refers to and encompasses any and all possible combinations ofone or more of the associated listed items. It will be furtherunderstood that the terms “includes,” “including,” “comprises,” and/or“comprising,” when used in this specification, specify the presence ofstated features, integers, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, integers, steps, operations, elements, components,and/or groups thereof. The term “exemplary” is used herein in the senseof “serving as an example, instance, or illustration” and not in thesense of “representing the best of its kind.”

FIG. 1A illustrates display device 100 in accordance with someembodiments. In some embodiments, display device 100 is configured to beworn on a head of a user (e.g., by having the form of spectacles oreyeglasses, as shown in FIG. 1A) or to be included as part of a helmetthat is to be worn by the user. When display device 100 is configured tobe worn on a head of a user or to be included as part of a helmet,display device 100 is called a head-mounted display. Alternatively,display device 100 is configured for placement in proximity of an eye oreyes of the user at a fixed location, without being head-mounted (e.g.,display device 100 is mounted in a vehicle, such as a car or anairplane, for placement in front of an eye or eyes of the user).

In some embodiments, display device 100 includes one or more componentsdescribed below with respect to FIG. 1B. In some embodiments, displaydevice 100 includes additional components not shown in FIG. 1B.

FIG. 1B is a block diagram of system 200 in accordance with someembodiments. The system 200 shown in FIG. 1B includes display device 205(which corresponds to display device 100 shown in FIG. 1A), imagingdevice 235, and input interface 240 that are each coupled to console210. While FIG. 1B shows an example of system 200 including one displaydevice 205, imaging device 235, and input interface 240, in otherembodiments, any number of these components may be included in system200. For example, there may be multiple display devices 205 each havingassociated input interface 240 and being monitored by one or moreimaging devices 235, with each display device 205, input interface 240,and imaging devices 235 communicating with console 210. In alternativeconfigurations, different and/or additional components may be includedin system 200. For example, in some embodiments, console 210 isconnected via a network (e.g., the Internet) to system 200 or isself-contained as part of display device 205 (e.g., physically locatedinside display device 205). In some embodiments, display device 205 isused to create mixed reality by adding in a view of the realsurroundings. Thus, display device 205 and system 200 described here candeliver virtual reality, mixed reality, and augmented reality.

In some embodiments, as shown in FIG. 1A, display device 205 is ahead-mounted display that presents media to a user. Examples of mediapresented by display device 205 include one or more images, video,audio, or some combination thereof. In some embodiments, audio ispresented via an external device (e.g., speakers and/or headphones) thatreceives audio information from display device 205, console 210, orboth, and presents audio data based on the audio information. In someembodiments, display device 205 immerses a user in a virtualenvironment.

In some embodiments, display device 205 also acts as an augmentedreality (AR) headset. In these embodiments, display device 205 augmentsviews of a physical, real-world environment with computer-generatedelements (e.g., images, video, sound, etc.). Moreover, in someembodiments, display device 205 is able to cycle between different typesof operation. Thus, display device 205 operate as a virtual reality (VR)device, an AR device, as glasses or some combination thereof (e.g.,glasses with no optical correction, glasses optically corrected for theuser, sunglasses, or some combination thereof) based on instructionsfrom application engine 255.

Display device 205 includes electronic display 215, one or moreprocessors 216, eye tracking module 217, adjustment module 218, one ormore locators 220, one or more position sensors 225, one or moreposition cameras 222, memory 228, inertial measurement unit (IMU) 230,or a subset or superset thereof (e.g., display device 205 withelectronic display 215, one or more processors 216, and memory 228,without any other listed components). Some embodiments of display device205 have different modules than those described here. Similarly, thefunctions can be distributed among the modules in a different mannerthan is described here.

One or more processors 216 (e.g., processing units or cores) executeinstructions stored in memory 228. Memory 228 includes high-speed randomaccess memory, such as DRAM, SRAM, DDR RAM or other random access solidstate memory devices; and may include non-volatile memory, such as oneor more magnetic disk storage devices, optical disk storage devices,flash memory devices, or other non-volatile solid state storage devices.Memory 228, or alternately the non-volatile memory device(s) withinmemory 228, includes a non-transitory computer readable storage medium.In some embodiments, memory 228 or the computer readable storage mediumof memory 228 stores programs, modules and data structures, and/orinstructions for displaying one or more images on electronic display215.

Electronic display 215 displays images to the user in accordance withdata received from console 210 and/or processor(s) 216. In variousembodiments, electronic display 215 may comprise a single adjustableelectronic display element or multiple adjustable electronic displayselements (e.g., a display for each eye of a user).

In some embodiments, the display element includes one or more lightemission devices and a corresponding array of emission intensity array.An emission intensity array is an array of electro-optic pixels,opto-electronic pixels, some other array of devices that dynamicallyadjust the amount of light transmitted by each device, or somecombination thereof. These pixels are placed behind one or more lenses.In some embodiments, the emission intensity array is an array of liquidcrystal based pixels in an LCD (a Liquid Crystal Display). Examples ofthe light emission devices include: an organic light emitting diode, anactive-matrix organic light-emitting diode, a light emitting diode, sometype of device capable of being placed in a flexible display, or somecombination thereof. The light emission devices include devices that arecapable of generating visible light (e.g., red, green, blue, etc.) usedfor image generation. The emission intensity array is configured toselectively attenuate individual light emission devices, groups of lightemission devices, or some combination thereof. Alternatively, when thelight emission devices are configured to selectively attenuateindividual emission devices and/or groups of light emission devices, thedisplay element includes an array of such light emission devices withouta separate emission intensity array.

One or more lenses direct light from the arrays of light emissiondevices (optionally through the emission intensity arrays) to locationswithin each eyebox and ultimately to the back of the user's retina(s).An eyebox is a region that is occupied by an eye of a user locatedproximity to display device 205 (e.g., a user wearing display device205) for viewing images from display device 205. In some cases, theeyebox is represented as a 10 mm×10 mm square. In some embodiments, theone or more lenses include one or more coatings, such as anti-reflectivecoatings.

In some embodiments, the display element includes an infrared (IR)detector array that detects IR light that is retro-reflected from theretinas of a viewing user, from the surface of the corneas, lenses ofthe eyes, or some combination thereof. The IR detector array includes anIR sensor or a plurality of IR sensors that each correspond to adifferent position of a pupil of the viewing user's eye. In alternateembodiments, other eye tracking systems may also be employed.

Eye tracking module 217 determines locations of each pupil of a user'seyes. In some embodiments, eye tracking module 217 instructs electronicdisplay 215 to illuminate the eyebox with IR light (e.g., via IRemission devices in the display element).

A portion of the emitted IR light will pass through the viewing user'spupil and be retro-reflected from the retina toward the IR detectorarray, which is used for determining the location of the pupil.Alternatively, the reflection off of the surfaces of the eye is used toalso determine location of the pupil. The IR detector array scans forretro-reflection and identifies which IR emission devices are activewhen retro-reflection is detected. Eye tracking module 217 may use atracking lookup table and the identified IR emission devices todetermine the pupil locations for each eye. The tracking lookup tablemaps received signals on the IR detector array to locations(corresponding to pupil locations) in each eyebox. In some embodiments,the tracking lookup table is generated via a calibration procedure(e.g., user looks at various known reference points in an image and eyetracking module 217 maps the locations of the user's pupil while lookingat the reference points to corresponding signals received on the IRtracking array). As mentioned above, in some embodiments, system 200 mayuse other eye tracking systems than the embedded IR one described above.

Adjustment module 218 generates an image frame based on the determinedlocations of the pupils. In some embodiments, this sends a discreteimage to the display that will tile subimages together thus a coherentstitched image will appear on the back of the retina. Adjustment module218 adjusts an output (i.e. the generated image frame) of electronicdisplay 215 based on the detected locations of the pupils. Adjustmentmodule 218 instructs portions of electronic display 215 to pass imagelight to the determined locations of the pupils. In some embodiments,adjustment module 218 also instructs the electronic display to not passimage light to positions other than the determined locations of thepupils. Adjustment module 218 may, for example, block and/or stop lightemission devices whose image light falls outside of the determined pupillocations, allow other light emission devices to emit image light thatfalls within the determined pupil locations, translate and/or rotate oneor more display elements, dynamically adjust curvature and/or refractivepower of one or more active lenses in the lens (e.g., microlens) arrays,or some combination thereof.

Optional locators 220 are objects located in specific positions ondisplay device 205 relative to one another and relative to a specificreference point on display device 205. A locator 220 may be a lightemitting diode (LED), a corner cube reflector, a reflective marker, atype of light source that contrasts with an environment in which displaydevice 205 operates, or some combination thereof. In embodiments wherelocators 220 are active (i.e., an LED or other type of light emittingdevice), locators 220 may emit light in the visible band (e.g., about400 nm to 750 nm), in the infrared band (e.g., about 750 nm to 1 mm), inthe ultraviolet band (about 100 nm to 400 nm), some other portion of theelectromagnetic spectrum, or some combination thereof.

In some embodiments, locators 220 are located beneath an outer surfaceof display device 205, which is transparent to the wavelengths of lightemitted or reflected by locators 220 or is thin enough to notsubstantially attenuate the wavelengths of light emitted or reflected bylocators 220. Additionally, in some embodiments, the outer surface orother portions of display device 205 are opaque in the visible band ofwavelengths of light. Thus, locators 220 may emit light in the IR bandunder an outer surface that is transparent in the IR band but opaque inthe visible band.

IMU 230 is an electronic device that generates calibration data based onmeasurement signals received from one or more position sensors 225.Position sensor 225 generates one or more measurement signals inresponse to motion of display device 205. Examples of position sensors225 include: one or more accelerometers, one or more gyroscopes, one ormore magnetometers, another suitable type of sensor that detects motion,a type of sensor used for error correction of IMU 230, or somecombination thereof. Position sensors 225 may be located external to IMU230, internal to IMU 230, or some combination thereof.

Based on the one or more measurement signals from one or more positionsensors 225, IMU 230 generates first calibration data indicating anestimated position of display device 205 relative to an initial positionof display device 205. For example, position sensors 225 includemultiple accelerometers to measure translational motion (forward/back,up/down, left/right) and multiple gyroscopes to measure rotationalmotion (e.g., pitch, yaw, roll). In some embodiments, IMU 230 rapidlysamples the measurement signals and calculates the estimated position ofdisplay device 205 from the sampled data. For example, IMU 230integrates the measurement signals received from the accelerometers overtime to estimate a velocity vector and integrates the velocity vectorover time to determine an estimated position of a reference point ondisplay device 205. Alternatively, IMU 230 provides the sampledmeasurement signals to console 210, which determines the firstcalibration data. The reference point is a point that may be used todescribe the position of display device 205. While the reference pointmay generally be defined as a point in space; however, in practice thereference point is defined as a point within display device 205 (e.g., acenter of IMU 230).

In some embodiments, IMU 230 receives one or more calibration parametersfrom console 210. As further discussed below, the one or morecalibration parameters are used to maintain tracking of display device205. Based on a received calibration parameter, IMU 230 may adjust oneor more IMU parameters (e.g., sample rate). In some embodiments, certaincalibration parameters cause IMU 230 to update an initial position ofthe reference point so it corresponds to a next calibrated position ofthe reference point. Updating the initial position of the referencepoint as the next calibrated position of the reference point helpsreduce accumulated error associated with the determined estimatedposition. The accumulated error, also referred to as drift error, causesthe estimated position of the reference point to “drift” away from theactual position of the reference point over time.

Imaging device 235 generates calibration data in accordance withcalibration parameters received from console 210. Calibration dataincludes one or more images showing observed positions of locators 220that are detectable by imaging device 235. In some embodiments, imagingdevice 235 includes one or more still cameras, one or more videocameras, any other device capable of capturing images including one ormore locators 220, or some combination thereof. Additionally, imagingdevice 235 may include one or more filters (e.g., used to increasesignal to noise ratio). Imaging device 235 is configured to optionallydetect light emitted or reflected from locators 220 in a field of viewof imaging device 235. In embodiments where locators 220 include passiveelements (e.g., a retroreflector), imaging device 235 may include alight source that illuminates some or all of locators 220, whichretro-reflect the light towards the light source in imaging device 235.Second calibration data is communicated from imaging device 235 toconsole 210, and imaging device 235 receives one or more calibrationparameters from console 210 to adjust one or more imaging parameters(e.g., focal length, focus, frame rate, ISO, sensor temperature, shutterspeed, aperture, etc.).

Input interface 240 is a device that allows a user to send actionrequests to console 210. An action request is a request to perform aparticular action. For example, an action request may be to start or endan application or to perform a particular action within the application.Input interface 240 may include one or more input devices. Example inputdevices include: a keyboard, a mouse, a game controller, data from brainsignals, data from other parts of the human body, or any other suitabledevice for receiving action requests and communicating the receivedaction requests to console 210. An action request received by inputinterface 240 is communicated to console 210, which performs an actioncorresponding to the action request. In some embodiments, inputinterface 240 may provide haptic feedback to the user in accordance withinstructions received from console 210. For example, haptic feedback isprovided when an action request is received, or console 210 communicatesinstructions to input interface 240 causing input interface 240 togenerate haptic feedback when console 210 performs an action.

Console 210 provides media to display device 205 for presentation to theuser in accordance with information received from one or more of:imaging device 235, display device 205, and input interface 240. In theexample shown in FIG. 1B, console 210 includes application store 245,tracking module 250, and application engine 255. Some embodiments ofconsole 210 have different modules than those described in conjunctionwith FIG. 1B. Similarly, the functions further described below may bedistributed among components of console 210 in a different manner thanis described here.

When application store 245 is included in console 210, application store245 stores one or more applications for execution by console 210. Anapplication is a group of instructions, that when executed by aprocessor, is used for generating content for presentation to the user.Content generated by the processor based on an application may be inresponse to inputs received from the user via movement of display device205 or input interface 240. Examples of applications include: gamingapplications, conferencing applications, video playback application, orother suitable applications.

When tracking module 250 is included in console 210, tracking module 250calibrates system 200 using one or more calibration parameters and mayadjust one or more calibration parameters to reduce error indetermination of the position of display device 205. For example,tracking module 250 adjusts the focus of imaging device 235 to obtain amore accurate position for observed locators on display device 205.Moreover, calibration performed by tracking module 250 also accounts forinformation received from IMU 230. Additionally, if tracking of displaydevice 205 is lost (e.g., imaging device 235 loses line of sight of atleast a threshold number of locators 220), tracking module 250re-calibrates some or all of system 200.

In some embodiments, tracking module 250 tracks movements of displaydevice 205 using second calibration data from imaging device 235. Forexample, tracking module 250 determines positions of a reference pointof display device 205 using observed locators from the secondcalibration data and a model of display device 205. In some embodiments,tracking module 250 also determines positions of a reference point ofdisplay device 205 using position information from the first calibrationdata. Additionally, in some embodiments, tracking module 250 may useportions of the first calibration data, the second calibration data, orsome combination thereof, to predict a future location of display device205. Tracking module 250 provides the estimated or predicted futureposition of display device 205 to application engine 255.

Application engine 255 executes applications within system 200 andreceives position information, acceleration information, velocityinformation, predicted future positions, or some combination thereof ofdisplay device 205 from tracking module 250. Based on the receivedinformation, application engine 255 determines content to provide todisplay device 205 for presentation to the user. For example, if thereceived information indicates that the user has looked to the left,application engine 255 generates content for display device 205 thatmirrors the user's movement in a virtual environment. Additionally,application engine 255 performs an action within an applicationexecuting on console 210 in response to an action request received frominput interface 240 and provides feedback to the user that the actionwas performed. The provided feedback may be visual or audible feedbackvia display device 205 or haptic feedback via input interface 240.

FIG. 2A illustrates a cross-section of conventional Fresnel lens 260. Insome embodiments, a Fresnel lens, such as conventional Fresnel lens 260,includes a plurality of Fresnel structures 262 (e.g., a plurality ofannular rings 262-1, 262-2, 262-3, and 262-4). As shown in FIG. 2A, eachFresnel structure 262 (e.g., Fresnel structure 262-2) has a slope facetand a draft facet. The draft facet is characterized by a draft angle(e.g., the draft facet is tilted by the draft angle from a referenceaxis). In some embodiments, the slope facet is characterized by a slopeangle (e.g., the slope facet is tilted by the slope angle from thereference axis). In conventional Fresnel lens 260, Fresnel structures262 (e.g., 262-1, 262-2, 262-3, and 262-4) have a same draft angle.

FIG. 2B illustrates a cross-section of Fresnel lens 270 with dynamicdraft in accordance with some embodiments. In Fresnel lens 270, thedraft angle of each Fresnel structure is based on a distance of theFresnel structure from a center of the lens. For example, as shown inFIG. 2C, a Fresnel structure located close to the center of the lens hasa draft facet that is steeper than a draft facet of a Fresnel structurelocated away from the center of the lens (e.g., a Fresnel structurelocated closer to the center of the lens has a smaller draft angle thana draft angle of a Fresnel structure located away from the center of thelens). In FIG. 2B, Fresnel structure 272 has a particular draft angle,and Fresnel structure 274 has a draft angle that is distinct from thedraft angle of Fresnel structure 272 (e.g., Fresnel structure 272 has adraft angle that is less than the draft angle of Fresnel structure 274).

FIG. 2C illustrates surface profiles of a conventional Fresnel lens anda Fresnel lens with dynamic draft in accordance with some embodiments.In FIG. 2C, the surface profiles are shown as functions of a distance rfrom a center of a lens. As explained above, a conventional Fresnel lenshas a constant draft angle, independent of a position of each Fresnelstructure (e.g., a distance from a center of the lens to the Fresnelstructure). A Fresnel lens with dynamic draft has Fresnel structureswith different draft angles, where the draft angle for each Fresnelstructure is based on a distance from a center of the lens to theFresnel structure. In FIG. 2C, the draft angle increases (e.g., thedraft facet becomes less steep) when the distance from the center of thelens increases.

FIGS. 2D and 2E illustrate interaction between incoming light and adraft facet in accordance with some embodiments.

FIG. 2D illustrates that incoming light is refracted on a slope facet ofa Fresnel structure. A portion of the light refracted on the slope facetimpinges on the draft facet of the Fresnel structure, and a portion ofthe light impinging on the draft facet is reflected by the draft facet(e.g., by total internal reflection), which increases stray light.

FIG. 2E illustrates that incoming light is refracted on the slope facetof a Fresnel structure. A portion of the incoming light impinges on thedraft facet of the Fresnel structure, and is reflected. A portion of thereflected light enters through the slope facet of an adjacent Fresnelstructure, which also increases stray light.

As shown in FIGS. 2D and 2E, interaction between incoming light and adraft facet increases stray light, thereby increasing optical artifacts.Such optical artifacts are reduced by using a Fresnel structure withdynamic draft, as shown in FIG. 2F.

FIG. 2F illustrates reduction in interaction between incoming light anda draft facet in accordance with some embodiments. In FIG. 2F, the draftangle is selected so that the draft facet is parallel to the lightrefracted on the slope facet. Thus, the light refracted on the slopefacet does not interact with the draft facet, which reduces stray light,thereby reducing optical artifacts.

FIG. 2G shows a cross-sectional view of a Fresnel lens with dynamicdraft in accordance with some embodiments. Light from a display deviceis focused by a Fresnel lens with dynamic draft. In some embodiments,the focused light is sent toward an eye of a user. As explained abovewith respect to FIG. 2F, the draft facets are angled so that interactionbetween the incoming light (after refraction on the slope facet) and thedraft facets is reduced or eliminated.

FIG. 2G also shows that a peripheral region of the lens (e.g., a regionthat is further away from the center of the lens) is used for focusinglight from a peripheral region of the display device, and a centralregion of the lens is used for focusing light from a central region ofthe display device. As explained above with respect to FIG. 2C, thedraft angle is selected based on a position of each Fresnel structure.For example, a Fresnel structure located closer to a center of the lenshas a small draft angle (which leads to a steep draft facet) and aFresnel structure located away from the center of the lens has a largedraft angle (which leads to a less steep draft facet). Thus, the largedraft angle in the peripheral region of the lens facilitates reductionof optical artifacts when transmitting light from the peripheral regionof the display device, and the small draft angle in the central regionof the lens facilitates reduction of optical artifacts when transmittinglight from the central region of the display device. Thus, the Fresnellens with dynamic draft, shown in FIG. 2G, is especially effective inreducing optical artifacts when imaging light from the display device.

FIGS. 2H and 2I show optical artifacts caused by a conventional Fresnellens and a Fresnel lens with dynamic draft in accordance with someembodiments.

FIG. 2H shows images of a white surface collected with a conventionalFresnel lens with constant draft and a Fresnel lens with dynamic draft.The image of a white surface collected with a conventional Fresnel lens(shown on the left side of FIG. 2H) shows periodic rings, which arecaused by the draft facets of the conventional Fresnel lens. Incomparison, in the image of a white surface collected with a Fresnellens with dynamic draft (shown on the right side of FIG. 2H), periodicrings are less visible.

FIG. 2I shows images of a display collected with a conventional Fresnellens with constant draft and a Fresnel lens with dynamic draft. Theimage of a display collected with a conventional Fresnel lens (shown onthe left side of FIG. 2I) shows periodic rings, similar to the imagecollected with a conventional Fresnel lens with constant draft, as shownin FIG. 2H. FIG. 2I also includes an enlarged view of a portion of theimage collected with the conventional Fresnel lens with constant draft,which better shows the periodic structures in the image collected withthe conventional Fresnel lens. In the image of a display collected witha Fresnel lens with dynamic draft (shown on the right side of FIG. 2I),the visibility of the periodic rings are reduced, similar to the imagecollected with a Fresnel lens with dynamic draft, as shown in FIG. 2H.

FIG. 3A is an isometric view of display device 300 in accordance withsome embodiments. In some other embodiments, display device 300 is partof some other electronic display (e.g., digital microscope, etc.). Insome embodiments, display device 300 includes light emission devicearray 310 and one or more lenses (e.g., lens 320). In some embodiments,display device 300 also includes an emission intensity array and an IRdetector array.

Light emission device array 310 emits image light and optional IR lighttoward the viewing user. Light emission device array 310 may be, e.g.,an array of LEDs, an array of microLEDs, an array of OLEDs, or somecombination thereof. Light emission device array 310 includes lightemission devices 312 that emit visible light (and optionally includesdevices that emit IR light).

The emission intensity array is configured to selectively attenuatelight emitted from light emission array 310. In some embodiments, theemission intensity array is composed of a plurality of liquid crystalcells or pixels, groups of light emission devices, or some combinationthereof. Each of the liquid crystal cells is, or in some embodiments,groups of liquid crystal cells are, addressable to have specific levelsof attenuation. For example, at a given time, some of the liquid crystalcells may be set to no attenuation, while other liquid crystal cells maybe set to maximum attenuation. In this manner the emission intensityarray is able to control what portion of the image light emitted fromlight emission device array 310 is passed to the one or more lenses(e.g., lens 320). In some embodiments, display device 300 uses theemission intensity array to facilitate providing image light to alocation of pupil 332 of eye 330 of a user, and minimize the amount ofimage light provided to other areas in the eyebox.

Similar to FIG. 2G, which illustrates that a lens is used to transmitlight from a display to an eye, in FIG. 3A, one or more lenses (e.g.,lens 320) receive the modified image light (e.g., attenuated light) fromthe emission intensity array (or directly from emission device array310), and directs the modified image light to a location of pupil 332.Lens 320 includes one or more diffractive optics. In some embodiments,the one or more lenses include one or more active lenses. An active lensis a lens whose lens curvature and/or refractive ability may bedynamically controlled (e.g., via a change in applied voltage). Anactive lens may be a liquid crystal lens, a liquid lens (e.g., usingelectro-wetting), or some other lens whose curvature and/or refractiveability may be dynamically controlled, or some combination thereof.Accordingly, in some embodiments, system 200 may dynamically adjust thecurvature and/or refractive ability of active lenslets to direct lightreceived from the emission device array 310 to pupil 332.

In some embodiments, lens 320 includes a Fresnel lens, described belowwith respect to FIGS. 3B-3J and 4A-4C. In some embodiments, one or moreof the lenses illustrated in FIGS. 3B-3J and 4A-4D include dynamicdraft.

An optional IR detector array detects IR light that has beenretro-reflected from the retina of eye 330, a cornea of eye 330, acrystalline lens of eye 330, or some combination thereof. The IRdetector array includes either a single IR sensor or a plurality of IRsensitive detectors (e.g., photodiodes). In some embodiments, the IRdetector array is separate from light emission device array 310. In someembodiments, the IR detector array is integrated into light emissiondevice array 310.

In some embodiments, light emission device array 310 and the emissionintensity array make up a display element. Alternatively, the displayelement includes light emission device array 310 (e.g., when lightemission device array 310 includes individually adjustable pixels)without the emission intensity array. In some embodiments, the displayelement additionally includes the IR array. In some embodiments, inresponse to a determined location of pupil 332, the display elementadjusts the emitted image light such that the light output by thedisplay element is refracted by one or more lenses (e.g., lens 320)toward the determined location of pupil 332, and not toward otherlocations in the eyebox.

FIG. 3B is an isometric view of lens 340 from a first direction (e.g., adirection from which first lens surface 346 of lens 340 is visible) inaccordance with some embodiments. Lens 340 includes first portion 342(e.g., a central portion) and second portion 344 (e.g., an annularportion) around first portion 342. First portion 342 of lens 340includes portion 346-1 of first lens surface 346. In some embodiments,portion 346-1 of first lens surface 346 is a flat surface. In someembodiments, portion 346-1 of first lens surface 346 is a Fresnelsurface (e.g., Fresnel structures arranged on a flat surface). Secondportion 344 of lens 340 includes portion 346-2 of first lens surface346. In some embodiments, portion 346-2 of first lens surface 346 is aconvex surface. In some embodiments, portion 346-2 of first lens surface346 is a Fresnel surface (e.g., Fresnel structures arranged on a convexsurface).

In some embodiments, Fresnel structures have a constant pitch (e.g., 50μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 150 μm, 200 μm, 250 μm, 300 μm,350 μm, 400 μm, 450 μm, 500 μm, 550 μm, 600 μm, 700 μm, 800 μm, 900 μm,1 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm, 2 mm, 3 mm, etc.).

The lens shown in FIG. 3B is axisymmetric (e.g., rotationally symmetricabout a center of the lens). Although the lens shown in FIG. 3B is acircular lens, in some embodiments, a portion of the circular lens iscut out (e.g., a rectangular portion of the lens, as shown in FIG. 3A,is used).

FIG. 3C is an isometric view of lens 340 shown in FIG. 3B from a seconddirection (e.g., a direction from which second lens surface 348 that isopposite to first lens surface 346 shown in FIG. 3B is visible) inaccordance with some embodiments. First portion 342 of lens 340 includesportion 348-1 of second lens surface 348. In some embodiments, portion348-1 of second lens surface 348 is a convex surface. In someembodiments, portion 348-1 of second lens surface 348 does not includeFresnel structures. Second portion 344 of lens includes portion 348-2 ofsecond lens surface 348. In some embodiments, portion 348-2 of secondlens surface 348 is a concave surface. In some embodiments, portion348-2 of second lens surface 348 is a Fresnel surface (e.g., a concavesurface with Fresnel structures).

FIG. 3D shows a plan view and a cross-sectional view of lens 340 shownin FIG. 3B. As explained above, lens 340 includes first portion 342 andsecond portion 344 around first portion 342. First portion 342 includesportion 346-1 of first lens surface 346, and portion 348-1 of secondlens surface 348 that is opposite to portion 346-1 of first lens surface346. Second portion 344 includes portion 346-2 of first lens surface346, and portion 348-2 of second lens surface 348 that is opposite toportion 346-2 of first lens surface 346. Portion 346-1 is defined by aFresnel surface profile (e.g., a surface profile that includes Fresnelstructures, such as Fresnel structures arranged on a flat surface).Portion 348-1 is defined by a smooth surface profile (e.g., a surfaceprofile that does not include Fresnel structures, such as a convexsurface without Fresnel structures). Portion 346-2 is defined by aFresnel surface profile (e.g., a surface profile that includes Fresnelstructures, such as Fresnel structures arranged on a convex surface).Portion 348-2 is defined by a Fresnel surface profile (e.g., a surfaceprofile that includes Fresnel structures, such as Fresnel structuresarranged on a concave surface).

As described above, the central region of lens 340 corresponding tofirst portion 342 includes Fresnel structures on only one of the twolens surfaces, first lens surface 346 and second lens surface 348. Thisreduces optical artifacts in lens 340, compared to a lens having Fresnelstructures on both lens surfaces. Because optical artifacts are reducedfor the central region, a user viewing an image through lens 340 is lesslikely to perceive optical artifacts. The annular region of lens 340corresponding to second portion 344 includes Fresnel structures on bothfirst lens surface 346 and second lens surface 348. This increasesrefraction of light passing through the annular region of lens 340.

In some embodiments, when lens 340 is used in a display device (e.g.,display device 300), lens 340 is positioned so that first lens surface346 faces light emission device array 310 (and second lens surface 348faces an eye of a user when the eye of the user is placed adjacent tothe display device). In some other embodiments, when lens 340 is used ina display device (e.g., display device 300), lens 340 is positioned sothat second lens surface 348 faces light emission device array 310 (andfirst lens surface 346 faces the eye of the user when the eye of theuser is placed adjacent to the display device).

In some embodiments, Fresnel structures on first lens surface 346 havedynamic draft. In some embodiments, Fresnel structures on second lenssurface 348 have dynamic draft. In some embodiments, Fresnel structureson first lens surface 346 have dynamic draft, and Fresnel structures onsecond lens surface 348 have constant draft. In some embodiments,Fresnel structures on second lens surface 348 have dynamic draft, andFresnel structures on first lens surface 346 have constant draft.

FIG. 3E is a cross-sectional view of lens 350 in accordance with someembodiments.

Lens 350 includes first portion 352 and second portion 354 around firstportion 352. First portion 352 includes portion 356-1 of first lenssurface 356, and portion 358-1 of second lens surface 358 that isopposite to portion 356-1 of first lens surface 356. Second portion 354includes portion 356-2 of first lens surface 356, and portion 358-2 ofsecond lens surface 358 that is opposite to portion 356-2 of first lenssurface 356. Portion 356-1 is defined by a Fresnel surface profile(e.g., a surface profile that includes Fresnel structures, such asFresnel structures arranged on a convex surface). Portion 358-1 isdefined by a smooth surface profile (e.g., a surface profile that doesnot include Fresnel structures, such as a convex surface without Fresnelstructures). Portion 356-2 is defined by a Fresnel surface profile(e.g., a surface profile that includes Fresnel structures, such asFresnel structures arranged on a convex surface). Portion 358-2 isdefined by a Fresnel surface profile (e.g., a surface profile thatincludes Fresnel structures, such as Fresnel structures arranged on aconcave surface).

In lens 350, first lens surface 356 transitions continuously fromportion 356-1 to portion 356-2. For example, in some embodiments, aslope of portion 356-1 adjacent to a junction between portion 356-1 andportion 356-2 is the same as a slope of portion 356-2 adjacent to thejunction between portion 356-1 and portion 356-2. In some embodiments, aderivative of the slope of portion 356-1 adjacent to a junction betweenportion 356-1 and portion 356-2 is the same as a derivative of the slopeof portion 356-2 adjacent to the junction between portion 356-1 andportion 356-2. In some embodiments, a second derivative of the slope ofportion 356-1 adjacent to a junction between portion 356-1 and portion356-2 is the same as a second derivative of the slope of portion 356-2adjacent to the junction between portion 356-1 and portion 356-2. Thistransition reduces optical artifacts and reduces the visibility of thetransition.

In some embodiments, when lens 350 is used in a display device (e.g.,display device 300), lens 350 is positioned so that first lens surface356 faces light emission device array 310 (and second lens surface 358faces an eye of a user when the eye of the user is placed adjacent tothe display device). In some other embodiments, when lens 350 is used ina display device (e.g., display device 300), lens 350 is positioned sothat second lens surface 358 faces light emission device array 310 (andfirst lens surface 356 faces the eye of the user when the eye of theuser is placed adjacent to the display device).

In some embodiments, Fresnel structures on first lens surface 356 havedynamic draft. In some embodiments, Fresnel structures on second lenssurface 358 have dynamic draft. In some embodiments, Fresnel structureson first lens surface 356 have dynamic draft, and Fresnel structures onsecond lens surface 358 have constant draft. In some embodiments,Fresnel structures on second lens surface 358 have dynamic draft, andFresnel structures on first lens surface 356 have constant draft.

In some embodiments, lens 350 in FIG. 3E provides a temporal field ofview of 70°, 71°, 72°, 73°, 74°, 75°, 76°, 77°, 78°, 79°, 80°, 90°, or100°0 (e.g., for an eye relief of 20 mm).

FIG. 3F is a cross-sectional view of lens 360 in accordance with someembodiments.

Lens 360 includes first portion 362 and second portion 364 around firstportion 362. First portion 362 includes portion 366-1 of first lenssurface 366, and portion 368-1 of second lens surface 368 that isopposite to portion 366-1 of first lens surface 366. Second portion 364includes portion 366-2 of first lens surface 366, and portion 368-2 ofsecond lens surface 368 that is opposite to portion 366-2 of first lenssurface 366. Portion 366-1 is defined by a Fresnel surface profile(e.g., a surface profile that includes Fresnel structures, such asFresnel structures arranged on a convex surface). Portion 368-1 isdefined by a smooth surface profile (e.g., a surface profile that doesnot include Fresnel structures, such as a flat surface without Fresnelstructures). Portion 366-2 is defined by a Fresnel surface profile(e.g., a surface profile that includes Fresnel structures, such asFresnel structures arranged on a convex surface). Portion 368-2 isdefined by a Fresnel surface profile (e.g., a surface profile thatincludes Fresnel structures, such as Fresnel structures arranged on aconcave surface).

In lens 360, first lens surface 366 transitions continuously fromportion 366-1 to portion 366-2. For example, in some embodiments, aslope of portion 366-1 adjacent to a junction between portion 366-1 andportion 366-2 is the same as a slope of portion 366-2 adjacent to thejunction between portion 366-1 and portion 366-2. In some embodiments, aderivative of the slope of portion 366-1 adjacent to a junction betweenportion 366-1 and portion 366-2 is the same as a derivative of the slopeof portion 366-2 adjacent to the junction between portion 366-1 andportion 366-2. In some embodiments, a second derivative of the slope ofportion 366-1 adjacent to a junction between portion 366-1 and portion366-2 is the same as a second derivative of the slope of portion 366-2adjacent to the junction between portion 366-1 and portion 366-2. Thistransition reduces optical artifacts and reduces the visibility of thetransition.

In some embodiments, second lens surface 368 transitions continuouslyfrom portion 368-1 to portion 368-2. For example, in some embodiments, aslope of portion 368-1 adjacent to a junction between portion 368-1 andportion 368-2 is the same as a slope of portion 368-2 adjacent to thejunction between portion 368-1 and portion 368-2. This transitionfurther reduces optical artifacts and reduces the visibility of thetransition.

In some embodiments, Fresnel structures on first lens surface 366 havedynamic draft. In some embodiments, Fresnel structures on second lenssurface 368 have dynamic draft. In some embodiments, Fresnel structureson first lens surface 366 have dynamic draft, and Fresnel structures onsecond lens surface 368 have constant draft. In some embodiments,Fresnel structures on second lens surface 368 have dynamic draft, andFresnel structures on first lens surface 366 have constant draft.

In some embodiments, lens 360 in FIG. 3F provides a temporal field ofview that is larger than the temporal field of view provided by lens 350in FIG. 3E. In some embodiments, lens 360 in FIG. 3F provides a temporalfield of view of 80°, 81°, 82°, 83°, 84°, 85°, 86°, 87°, 88°, 89°, 90°,or 100° (e.g., for an eye relief of 20 mm).

FIG. 3G shows Fresnel structures of lens 360 shown in FIG. 3F inaccordance with some embodiments. In some embodiments, lens 360 includesFresnel structures smaller than the Fresnel structures illustrated inFIG. 3G. In some embodiments, lens 360 includes Fresnel structureslarger than the Fresnel structures illustrated in FIG. 3G.

As explained above, portion 366-1 is defined by a Fresnel surfaceprofile (e.g., a surface profile that includes Fresnel structures, suchas Fresnel structures arranged on a convex surface). Portion 368-1 isdefined by a smooth surface profile (e.g., a surface profile that doesnot include Fresnel structures, such as a flat surface without Fresnelstructures). Portion 366-2 is defined by a Fresnel surface profile(e.g., a surface profile that includes Fresnel structures, such asFresnel structures arranged on a convex surface). Portion 368-2 isdefined by a Fresnel surface profile (e.g., a surface profile thatincludes Fresnel structures, such as Fresnel structures arranged on aconcave surface).

In some embodiments, when lens 360 is used in a display device (e.g.,display device 300), lens 360 is positioned so that first lens surface366 faces light emission device array 310 (and second lens surface 368faces an eye of a user when the eye of the user is placed adjacent tothe display device). In some other embodiments, when lens 360 is used ina display device (e.g., display device 300), lens 360 is positioned sothat second lens surface 368 faces light emission device array 310 (andfirst lens surface 366 faces the eye of the user when the eye of theuser is placed adjacent to the display device).

FIG. 3H is a cross-sectional view of lens 370 in accordance with someembodiments.

Lens 370 includes first portion 372 and second portion 374 around firstportion 372. First portion 372 includes portion 376-1 of first lenssurface 376, and portion 378-1 of second lens surface 378 that isopposite to portion 376-1 of first lens surface 376. Second portion 374includes portion 376-2 of first lens surface 376, and portion 378-2 ofsecond lens surface 378 that is opposite to portion 376-2 of first lenssurface 376. Portion 376-1 is defined by a Fresnel surface profile(e.g., a surface profile that includes Fresnel structures, such asFresnel structures arranged on a convex surface). Portion 378-1 isdefined by a smooth surface profile (e.g., a surface profile that doesnot include Fresnel structures, such as a convex surface without Fresnelstructures). Portion 376-2 is defined by a Fresnel surface profile(e.g., a surface profile that includes Fresnel structures, such asFresnel structures arranged on a convex surface). Portion 378-2 isdefined by a Fresnel surface profile (e.g., a surface profile thatincludes Fresnel structures, such as Fresnel structures arranged on aconcave surface). In some embodiments, second lens surface 378(including both portions 378-1 and 378-2) is described by a high-orderpolynomial such that second lens surface 378 includes a convex surfacein portion 378-1 and transitions, after an inflection point, to aconcave surface in portion 378-2. For example, second lens surface 378is defined by a fourth-order polynomial, such as z₁(r)=a₁+b₁×r²+c₁×r⁴,where r is a radial position from a center of the lens, z₁ is a heightof second lens surface 378 at the radial position r, and a₁, b₁, and c₁are coefficients. In some cases, second lens surface 378 is defined by ahigher order polynomial (e.g., a sixth-order polynomial, an eight-orderpolynomial, a tenth-order polynomial, etc.) In some embodiments, Fresnelfacets are gradually tapered into portion 378-2 near this inflectionpoint. In some embodiments, first lens surface 376 (including bothportions 376-1 and 376-2) is described by a high-order polynomial suchthat first lens surface 376 includes a convex surface in portion 376-1,and transitions to a less-steep surface near a junction between portion376-1 and 376-2 (e.g., the slope decreases near the junction betweenportion 376-1 and 376-2) and to another convex surface in portion 376-2.For example, first lens surface 376 is defined by a sixth-orderpolynomial, such as z₂(r)=a₂+b₂×r²+c×r⁴+d×r⁶, where z₂ is a height offirst lens surface 376 at the radial position r, and a₂, b₂, c₂, and dare coefficients. In some cases, first lens surface 376 is defined by ahigher order polynomial (e.g., an eight-order polynomial, a tenth-orderpolynomial, a twelfth-order polynomial, etc.).

In lens 370, first lens surface 376 transitions continuously fromportion 376-1 to portion 376-2. For example, in some embodiments, aslope of portion 376-1 adjacent to a junction between portion 376-1 andportion 376-2 is the same as a slope of portion 376-2 adjacent to thejunction between portion 376-1 and portion 376-2. In some embodiments, aderivative of the slope of portion 376-1 adjacent to a junction betweenportion 376-1 and portion 376-2 is the same as a derivative of the slopeof portion 376-2 adjacent to the junction between portion 376-1 andportion 376-2. In some embodiments, a second derivative of the slope ofportion 376-1 adjacent to a junction between portion 376-1 and portion376-2 is the same as a second derivative of the slope of portion 376-2adjacent to the junction between portion 376-1 and portion 376-2. Thistransition reduces optical artifacts and reduces the visibility of thetransition.

In some embodiments, second lens surface 378 transitions continuouslyfrom portion 378-1 to portion 378-2. For example, in some embodiments, aslope of portion 378-1 adjacent to a junction between portion 378-1 andportion 378-2 is the same as a slope of portion 378-2 adjacent to thejunction between portion 378-1 and portion 378-2. In some embodiments, aderivative of the slope of portion 378-1 adjacent to a junction betweenportion 378-1 and portion 378-2 is the same as a derivative of the slopeof portion 378-2 adjacent to the junction between portion 378-1 andportion 378-2. In some embodiments, a second derivative of the slope ofportion 378-1 adjacent to a junction between portion 378-1 and portion378-2 is the same as a second derivative of the slope of portion 378-2adjacent to the junction between portion 378-1 and portion 378-2. Thistransition further reduces optical artifacts and reduces the visibilityof the transition.

In some embodiments, when lens 370 is used in a display device (e.g.,display device 300), lens 370 is positioned so that first lens surface376 faces light emission device array 310 (and second lens surface 378faces an eye of a user when the eye of the user is placed adjacent tothe display device). In some other embodiments, when lens 370 is used ina display device (e.g., display device 300), lens 370 is positioned sothat second lens surface 378 faces light emission device array 310 (andfirst lens surface 376 faces the eye of the user when the eye of theuser is placed adjacent to the display device).

In some embodiments, Fresnel structures on first lens surface 376 havedynamic draft. In some embodiments, Fresnel structures on second lenssurface 378 have dynamic draft. In some embodiments, Fresnel structureson first lens surface 376 have dynamic draft, and Fresnel structures onsecond lens surface 378 have constant draft. In some embodiments,Fresnel structures on second lens surface 378 have dynamic draft, andFresnel structures on first lens surface 376 have constant draft.

In some embodiments, lens 370 in FIG. 3H provides a temporal field ofview of 70°, 71°, 72°, 73°, 74°, 75°, 76°, 77°, 78°, 79°, 80°, 90°, or100° (e.g., for an eye relief of 20 mm).

FIG. 31 is a cross-sectional view of lens 380 in accordance with someembodiments. Lens 380 is a combination of two component lenses, eachcomponent lens corresponding to a portion of lens 370 shown in FIG. 3H.In some embodiments, a first component lens is used for projecting animage toward one eye (e.g., a left eye) and a second component lens isused for projecting an image toward the other eye (e.g., a right eye).In some embodiments, the two component lenses are fused together, asshown in FIG. 3I. In some embodiments, the two component lenses areseparate from each other (e.g., the first component lens is separatefrom the second component lens).

FIG. 3J is a cross-sectional view of lens 390 in accordance with someembodiments.

Lens 390 is defined by a first lens surface (e.g., surface 396) and asecond lens surface (e.g., surface 398) opposite to the first lenssurface. The lens includes a first portion (e.g., a combination of 392-1and 394-1) and a second portion (e.g., a combination of 392-2 and 394-2)that is distinct from the first portion and is coupled with the firstportion. The first portion of the lens (e.g., the combination of 392-1and 394-1) includes a first sub-portion (e.g., 392-1) of the firstportion of the lens and a second sub-portion (e.g., 394-1), of the firstportion of the lens, located around the first sub-portion of the firstportion of the lens. The first sub-portion (e.g., 392-1) of the firstportion of the lens includes a first surface portion (e.g., surfaceportion 396-1) of the first lens surface. The second sub-portion (e.g.,394-1) of the first portion of the lens is defined by a second surfaceportion (e.g., surface portion 396-2) of the first lens surface and athird surface (e.g., surface 395) that is opposite to the second surfaceportion of the first lens surface. The second portion of the lens (e.g.,the combination of 392-2 and 394-2) includes a first sub-portion (e.g.,392-2) of the second portion of the lens and a second sub-portion (e.g.,394-2), of the second portion of the lens, located around the firstsub-portion of the second portion of the lens. The first sub-portion(e.g., 392-2) of the second portion of the lens includes a first surfaceportion (e.g., surface portion 398-1) of the second lens surface. Thesecond sub-portion (e.g., 394-2) of the second portion of the lens isdefined by a second surface portion (e.g., surface portion 398-2) of thesecond lens surface and a fourth surface (e.g., surface 397) that isopposite to the second surface portion of the second lens surface. Thesecond sub-portion (e.g., 394-1) of the first portion of the lens isseparate from the second sub-portion (e.g., 394-2) of the second portionof the lens. The third surface is distinct from the fourth surface. Thefirst lens surface (e.g., surface 396) is defined by a Fresnel surfaceprofile over the first surface portion and the second surface portion ofthe first lens surface (e.g., Fresnel structures are arranged on a flatsurface over the first surface portion and the second surface portion ofthe first lens surface). The second lens surface (e.g., surface 398) isdefined by a smooth surface profile over the first surface portion andthe second surface portion of the second lens surface (e.g., a concavelens surface). In some embodiments, the third lens surface (e.g.,surface 395) is defined by a smooth lens surface (e.g., a convex lenssurface). In some embodiments, the fourth lens surface (e.g., surface397) is defined by a Fresnel surface profile (e.g., Fresnel structuresarranged on a convex surface).

In some embodiments, Fresnel structures on lens surface 396 have dynamicdraft. In some embodiments, Fresnel structures on lens surface 397 havedynamic draft. In some embodiments, Fresnel structures on lens surface396 have dynamic draft, and Fresnel structures on lens surface 397 haveconstant draft. In some embodiments, Fresnel structures on lens surface397 have dynamic draft, and Fresnel structures on lens surface 396 haveconstant draft.

In some embodiments, lens 390 in FIG. 3J provides a temporal field ofview of 70°, 71°, 72°, 73°, 74°, 75°, 76°, 77°, 78°, 79°, 80°, 90°, or100° (e.g., for an eye relief of 20 mm).

FIG. 4A shows an isometric view of a lens in accordance with someembodiments. The lens shown in FIG. 4A is axisymmetric (e.g.,rotationally symmetric about a center of the lens). Although the lensshown in FIG. 4A is a circular lens, in some embodiments, a portion ofthe circular lens is cut out (e.g., a rectangular portion of the lens,as shown in FIG. 3A, is used).

FIG. 4B shows a plan view and a cross-sectional view of the lens shownin FIG. 4A. Line AA′ on the plan view represents a plane upon which thecross-sectional view is taken. The cross-sectional view of the lens isillustrated in detail in FIG. 4C.

FIG. 4C shows a cross-sectional view of the lens shown in FIG. 4A.

The lens is defined by first lens surface 440 and second lens surface450 opposite to the first lens surface. First portion 442 of first lenssurface 440 is defined by a smooth surface profile function. Secondportion 444 of first lens surface 440 is defined by a Fresnel surfaceprofile function. Second portion 444 of first lens surface 440 is aroundfirst portion 442 of first lens surface 440 (e.g., second portion 444 offirst lens surface 440 corresponds to concentric annular sections, ofthe lens, that are offset from one another).

In some embodiments, a width (e.g., a diameter) of first portion 442 offirst lens surface 440 is at least 10% of a width (e.g., a diameter) ofthe lens. In some embodiments, the width (e.g., the diameter) of firstportion 442 of first lens surface 440 is at least 20% of the width(e.g., the diameter) of the lens. In some embodiments, the width (e.g.,the diameter) of first portion 442 of first lens surface 440 is at least30% of the width (e.g., the diameter) of the lens. In some embodiments,the width (e.g., the diameter) of first portion 442 of first lenssurface 440 is at least 40% of the width (e.g., the diameter) of thelens. In some embodiments, the width (e.g., the diameter) of firstportion 442 of first lens surface 440 is at least 50% of the width(e.g., the diameter) of the lens. In some embodiments, the width (e.g.,the diameter) of first portion 442 of first lens surface 440 is at least60% of the width (e.g., the diameter) of the lens. In some embodiments,the width (e.g., the diameter) of first portion 442 of first lenssurface 440 is at least 70% of the width (e.g., the diameter) of thelens. In some embodiments, the width (e.g., the diameter) of firstportion 442 of first lens surface 440 is at least 80% of the width(e.g., the diameter) of the lens.

As used herein, a smooth surface profile function refers to a surfaceprofile function whose derivative is continuous (e.g., when a surfaceprofile is defined as a function of a radial position a, such as F(a),the derivative of F(a), such as F′(a), is continuous). In someembodiments, a Fresnel surface profile function is characterized bydiscontinuities in a derivative of the Fresnel surface profile function(e.g., when a surface profile is defined as a function of a radialposition a, such as F(a), the derivative of F(a), such as F′(a), hasdiscontinuities). In some embodiments, a smooth surface profile functionis characterized by a derivative of the smooth surface profile functionhaving zero and either positive or negative values from a center of thelens to one end of the lens (e.g., the derivative of the smooth surfaceprofile function has zero and negative values only from the center ofthe lens to one end of the lens), and a Fresnel surface profile functionis characterized by a derivative of the Fresnel surface profile functionhaving both positive and negative values from the center of the lens toone end of the lens.

In some embodiments, the Fresnel surface profile function definesgrooves of a same height. In some embodiments, the Fresnel surfaceprofile function defines grooves of a same width.

In some embodiments, a height of first portion 442 (e.g., a differencebetween a center thickness of lens 430 and a thickness of lens 430 at ajunction between first portion 442 and second portion 444) is greaterthan any groove height (e.g., a vertical distance, parallel to an axisof lens 430, between a peak and a valley of a groove defined in secondportion 444). In some embodiments, the height of first portion 442 is atleast twice any groove height. In some embodiments, the height of firstportion 442 is at least three times any groove height. In someembodiments, the height of first portion 442 is at least five times anygroove height. In some embodiments, the height of first portion 442 isat least ten times any groove height.

FIG. 4D shows an isometric view of a cylindrical lens in accordance withsome embodiments. The lens in FIG. 4D has a cross-section thatcorresponds to the cross-section shown in FIG. 4C in only one direction.

The lens in FIG. 4D focuses light along a first direction, but does notfocus light along a second direction that is perpendicular to the firstdirection. Thus, the lens in FIG. 4C performs like a cylindrical lens.

In some embodiments, Fresnel structures in the lens shown in FIG. 4Dhave dynamic draft.

FIG. 5A illustrates an exemplary surface profile in accordance with someembodiments.

In FIG. 5A, the smooth lens surface transitions into the Fresnel lenssurface in a way so that the smooth lens surface and the Fresnel lenssurface are continuous and their slopes also match at a junction of thesmooth lens surface and the Fresnel lens surface. It has been found thatwhen the slope of the smooth lens surface and the slope of the Fresnellens surface match at the junction, the transition becomes opticallyseamless. This reduces or eliminates artifacts at the transition. Thoseskilled in the art will recognize that maintaining higher-ordercontinuities (e.g. continuities in 2^(nd) and/or 3^(rd) derivatives)further reduces artifacts (e.g. ripples in the distortion) at thetransition. Thus, in some embodiments, a second derivative of the smoothlens surface and a second derivative of the Fresnel lens surface matchat the junction. In some embodiments, a third derivative of the smoothlens surface and a third derivative of the Fresnel lens surface match atthe junction.

FIGS. 5B-5D illustrate exemplary surface profiles in accordance withsome embodiments. In FIGS. 5B-5D, the smooth lens surface transitionsinto the Fresnel lens surface in a way so that the smooth lens surfaceand the Fresnel lens surface are continuous but their slopes do notmatch at the junction of the smooth lens surface and the Fresnel lenssurface. In these lenses, the abrupt change in the slope causes animaging artifact. Ray bundles that straddle this discontinuity split todifferent portions of the display, which increases the visibility of thetransition.

In light of these principles, we now turn to certain embodiments.

In accordance with some embodiments, a lens includes an opticallytransparent substrate (e.g., a substrate made of glass, such as N-BK7,N-SF11, and F2; barium borate; barium fluoride; magnesium fluoride;sapphire; calcium fluoride; fused silica; calcite; etc.) having a firstlens surface and a second lens surface opposite to the first lenssurface (e.g., lens 430 in FIG. 4C has first lens surface 440 and secondlens surface 450). The first lens surface includes a plurality ofFresnel structures (e.g., first lens surface 440 includes Fresnelstructures in portion 444). A respective Fresnel structure of theplurality of Fresnel structures includes a slope facet and a draft facet(e.g., Fresnel structure 272 in FIG. 2A has a slope facet and a draftfacet). The draft facet is characterized by a draft angle. The draftangle of the respective Fresnel structure is based on a distance of therespective Fresnel structure from a center of the lens.

In some embodiments, the second lens surface does not include anyFresnel structures (e.g., lens 430 in FIG. 4C). In some embodiments, thesecond lens surface includes a plurality of Fresnel structures (e.g.,lens 340 in FIG. 3D). In some embodiments, the draft angle of arespective Fresnel structure on the second lens surface is based on adistance of the respective Fresnel structure from the center of thelens.

In some embodiments, the plurality of Fresnel structures includes afirst Fresnel structure and a second Fresnel structure (e.g., Fresnelstructure 272 and Fresnel structure 274 in FIG. 2B). The draft facet ofthe first Fresnel structure has a first draft angle (e.g., Fresnelstructure 272 has a small draft angle). The draft facet of the secondFresnel structure has a second draft angle that is distinct from thefirst draft angle (e.g., Fresnel structure 274 has a large draft angle).

In some embodiments, the lens is configured to focus light impinging onthe first lens surface (e.g., the lens is a converging lens, as shown inFIG. 2G).

In some embodiments, the draft angle of the respective Fresnel structureis selected, based on the distance of the respective Fresnel structurefrom the center of the lens, to reduce interaction of light impinging onthe first lens surface and the draft facet of the respective Fresnelstructure (e.g., as shown in FIG. 2C, the draft angle changes as afunction of the distance of the respective Fresnel structure from thecenter of the lens).

In some embodiments, the lens includes a first portion (e.g., 362 inFIG. 3G); and a second portion that is distinct from the first portionand is located around the first portion (e.g., 364 in FIG. 3G). Thefirst lens surface for the first portion of the lens (e.g., 366-1) isdefined by a Fresnel surface profile. The second lens surface for thefirst portion of the lens (e.g., 368-1) is defined by a smooth surfaceprofile function. The first lens surface for a second portion of thelens (e.g., 366-2) is defined by a Fresnel surface profile. The secondlens surface for the second portion of the lens (e.g., 368-2) is definedby a Fresnel surface profile.

In some embodiments, the first lens surface for the second portion ofthe lens extends from the first lens surface for the first portion ofthe lens, and the second lens surface for the second portion of the lensextends from the second lens surface for the first portion of the lens.For example, in FIG. 3G, portion 366-2 of first lens surface 366 extendsfrom portion 366-1 of first lens surface 366 and portion 368-2 of secondlens surface 368 extends from portion 368-1 of second lens surface 368.

In some embodiments, the second portion of the lens corresponds to oneor more portions of a convex-concave lens. For example, in FIG. 3H,second portion 374 is defined by convex surface 376-2 and concavesurface 378-2.

In some embodiments, the first portion of the lens corresponds to one ormore portions of a plano-convex lens. For example, in FIG. 3F, firstportion 362 is defined by convex surface 366-1 and flat surface 368-1.In another example, in FIG. 3D, first portion 342 is defined by flatsurface 346-1 and convex surface 348-1.

In some embodiments, the second portion of the lens corresponds to oneor more portions of a convex-concave lens. A convex surface of thesecond portion of the lens extends from a planar surface of the firstportion of the lens. For example, in FIG. 3D, second portion 344 isdefined by concave surface 348-2 and convex surface 346-2 that extendsfrom flat surface 346-1.

In some embodiments, the second portion of the lens corresponds to oneor more portions of a convex-concave lens. A concave surface of thesecond portion of the lens extends from a planar surface of the firstportion of the lens. For example, in FIG. 3F, second portion 364 isdefined by convex surface 366-2 and concave surface 368-2 that extendsfrom flat surface 368-1.

In some embodiments, the first portion of the lens corresponds to one ormore portions of a convex-convex lens. For example, in FIG. 3E, firstportion 352 is defined by convex surface 356-1 and convex surface 358-1.

In some embodiments, the second lens surface is defined by a polynomialthat includes a convex surface for the first portion of the lens and aconcave surface for the second portion of the lens (e.g., second lenssurface 378, in FIG. 3H, that includes a convex surface in first portion378-1 and a concave surface in second portion 378-2). In someembodiments, the first lens surface is defined by a polynomial thatincludes a convex surface for the first portion of the lens and a convexsurface for the second portion of the lens (e.g., first lens surface376-1, in FIG. 3H, that includes a convex surface in first portion 376-1and a convex surface in second portion 376-2).

In some embodiments, a first portion of the first lens surface (e.g.,portion 442 in FIG. 4C) is defined by a smooth surface profile function.A second portion of the first lens surface (e.g., portion 444 in FIG.4C) is defined by a Fresnel surface profile function. The second portionof the first lens surface is around the first portion of the first lenssurface. For example, the first portion of the first lens surface doesnot include any Fresnel structure, and the second portion of the firstlens surface includes a plurality of Fresnel structures.

In some embodiments, the second lens surface includes a plurality ofFresnel structures. In some embodiments, the second lens surface doesnot include any Fresnel structure.

In some embodiments, the first portion and the second portion of thefirst lens surface are defined by a sum of two surface profilefunctions. A first surface profile function of the two surface profilefunctions defines a smooth surface profile across the first portion andthe second portion of the first lens surface. A second surface profilefunction of the two surface profile functions defines: a smooth surfaceprofile across a first portion of the first lens surface; and a Fresnelsurface profile across a second portion of the first lens surface.

In some embodiments, a derivative (e.g., a first derivative) of thefirst surface profile function is continuous across of the first portionand the second portion of the first lens surface. A derivative (e.g., afirst derivative) of the second surface profile function is continuousacross the first portion of the first lens surface.

In some embodiments, a second derivative of the first surface profilefunction is continuous across the first portion and the second portionof the first lens surface, and a second derivative of the second surfaceprofile function is continuous across the first portion of the firstlens surface.

In some embodiments, the smooth surface profile, of the second surfaceprofile function, across the first portion of the first lens surface isflat.

In some embodiments, a derivative of the second surface profile functionhas discontinuities across the second portion of the first lens surface(e.g., the second portion has Fresnel structures).

In accordance with some embodiments, a display device (e.g., displaydevice 300 in FIG. 3A) includes the lens discussed above (e.g., lens 320in FIG. 3A). The display device also includes an array of light emittingdevices (e.g., an array of light emitting devices 310 in FIG. 3A)coupled with the lens for outputting light through the lens.

In some embodiments, the display device is a head-mounted display device(e.g., display device 100 in FIG. 1A).

In some embodiments, the array of light emitting devices is configuredto output light and transmit the light through the lens toward an eye ofa user (e.g., eye 330 in FIG. 3A) when the display device is worn on ahead of the user.

Although some of various drawings illustrate a number of logical stagesin a particular order, stages which are not order dependent may bereordered and other stages may be combined or broken out. While somereordering or other groupings are specifically mentioned, others will beapparent to those of ordinary skill in the art, so the ordering andgroupings presented herein are not an exhaustive list of alternatives.Moreover, it should be recognized that the stages could be implementedin hardware, firmware, software or any combination thereof.

The foregoing description, for purpose of explanation, has beendescribed with reference to specific embodiments. However, theillustrative discussions above are not intended to be exhaustive or tolimit the scope of the claims to the precise forms disclosed. Manymodifications and variations are possible in view of the aboveteachings. The embodiments were chosen in order to best explain theprinciples underlying the claims and their practical applications, tothereby enable others skilled in the art to best use the embodimentswith various modifications as are suited to the particular usescontemplated.

1. A lens, comprising: an optically transparent substrate having a firstlens surface and a second lens surface opposite to the first lenssurface, wherein: the first lens surface includes a plurality of Fresnelstructures; a respective Fresnel structure of the plurality of Fresnelstructures includes a slope facet and a draft facet, wherein the draftfacet is characterized by a draft angle; the draft angle of therespective Fresnel structure is based on a distance of the respectiveFresnel structure from a center of the lens; the optically transparentsubstrate has a central portion and a peripheral portion that isdistinct from the central portion and is located around the centralportion; the first lens surface for the central portion of the lens isdefined by a Fresnel surface profile; the second lens surface for thecentral portion of the lens is defined by a smooth surface profile; thefirst lens surface for the peripheral portion of the lens has a convexshape and is defined by a Fresnel surface profile; and the second lenssurface for the peripheral portion of the lens has a concave shape andis defined by a Fresnel surface profile.
 2. The lens of claim 1,wherein: the plurality of Fresnel structures includes a first Fresnelstructure and a second Fresnel structure; the draft facet of the firstFresnel structure has a first draft angle; and the draft facet of thesecond Fresnel structure has a second draft angle that is distinct fromthe first draft angle.
 3. The lens of claim 1, wherein: the lens isconfigured to focus light impinging on the first lens surface.
 4. Thelens of claim 1, wherein: the draft angle of the respective Fresnelstructure is selected, based on the distance of the respective Fresnelstructure from the center of the lens, to reduce interaction of lightimpinging on the first lens surface and the draft facet of therespective Fresnel structure.
 5. (canceled)
 6. The lens of claim 1,wherein the first lens surface for the peripheral portion of the lens isconnected to the first lens surface for the central portion of the lens,and the second lens surface for the peripheral portion of the lens isconnected to the second lens surface for the central portion of thelens.
 7. The lens of claim 1, wherein: the peripheral portion of thelens corresponds to one or more portions of a convex-concave lens. 8.The lens of claim 1, wherein: the central portion of the lenscorresponds to one or more portions of a plano-convex lens.
 9. The lensof claim 8, wherein: the peripheral portion of the lens corresponds toone or more portions of a convex-concave lens; and a convex surface ofthe peripheral portion of the lens extends from a planar surface of thecentral portion of the lens.
 10. The lens of claim 8, wherein: theperipheral portion of the lens corresponds to one or more portions of aconvex-concave lens; and a concave surface of the peripheral portion ofthe lens extends from a planar surface of the central portion of thelens.
 11. The lens of claim 1, wherein: the central portion of the lenscorresponds to one or more portions of a convex-convex lens.
 12. Thelens of claim 1, wherein: the second lens surface is defined by apolynomial that includes a convex surface for the central portion of thelens and a concave surface for the peripheral portion of the lens; andthe first lens surface is defined by a polynomial that includes a convexsurface for the central portion of the lens and a convex surface for theperipheral portion of the lens.
 13. (canceled)
 14. (canceled) 15.(canceled)
 16. (canceled)
 17. (canceled)
 18. A display device,comprising: the lens of claim 1; and an array of light emitting devicescoupled with the lens for outputting light through the lens.
 19. Thedisplay device of claim 18, wherein the display device is a head-mounteddisplay device.
 20. The display device of claim 19, wherein the array oflight emitting devices is configured to output light and transmit thelight through the lens toward an eye of a user when the display deviceis worn on a head of the user.